Obesity has been evidenced to be a major risk factor for inflammatory skin diseases, while the skin microbiome is known to harbour site-specific microbial communities that are influenced by biophysical properties, such as moisture, sebum, and skin surface acidity (pH).
However, little is known about the link between BMI and facial skin physiological parameters, particularly facial skin microbiome.
To investigate the correlations, a study including 198 healthy Chinese women, aged 18 to 35 years and living in Shanghai, was conducted in 2021.
The study was funded by Shandong Freda Biotech Co Ltd and Collaborative Innovation Center of Fragrance Flavour and Cosmetics.
The participants were categorised into three groups, namely lean (B1), normal weight (B2), and overweight and obese (B3).
The proportions of B2 and B3 were 70% and 10% respectively, which is consistent with figures reported in the 2021 China Population Health Data Report.
An analysis of the participants’ cheek skin found that the physiological parameters of B3 were significantly different from B1 and B2. In contrast, there was no significant divergence between B1 and B2.
Compared to B1 and B2, B3 exhibited a significant increase (p = 0.009) in trans-epidermal water loss (TEWL), indicating that skin barrier function in this group was impaired.
In addition, skin haemoglobin content significantly increased (p = 0.004) while skin surface pH significantly decreased (p = 0.007) in those with high BMI.
There was no important difference among the three groups in terms of skin firmness, skin melanin content, and elasticity value.
Furthermore, the findings revealed that BMI also causes changes in the alpha-diversity of bacteria in facial skin.
Specifically, B3 had higher abundances of Streptococcus (p = 0.031), Corynebacterium (p = 0.024), Malassezia (p = 0.003) and Candida (p = 0.016), and lower abundances of Neisseriaceae and Cutaneotrichosporon.
Notably, skin surface pH was significantly and negatively correlated with the relative abundances of Malassezia, Candida, and Cladosporium, whereas the abundance of Malassezia was positively associated with the abundances of Staphylococcus and Corynebacterium.
“These results showed that BMI is associated with differences in the biophysical properties and microbiome of facial skin. A high BMI affects the integrity of skin barrier, and alters the skin flora diversity and species composition.
“Many studies have proved that skin diseases or even systemic diseases can occur when the skin barrier is broken, or when the balance between commensal microorganisms, including bacteria and fungi, and pathogens is disturbed,” the authors wrote.
Role of fungi
Past research on the associations between BMI and the skin microbiota has mainly focused on bacteria but recent studies have shown that fungi play an important role in maintaining the balance of the skin microbiota.
Compared with normal or lean individuals, people who are obese tend to sweat more.
The increased subcutaneous fat also increases the friction and moisture content of the skin, causing obese individuals to be more vulnerable to skin diseases, such as secondary bacterial infections, candidiasis, and dermatophyte overgrowth.
In this study, it was discovered that the abundance of Malassezia and Candida rose significantly with increasing BMI.
Malassezia is the dominant fungal genus of the skin, and a large number of studies have found it to be associated with many skin conditions, including lichen planus, seborrheic dermatitis, and psoriasis.
There have also been reports that Candida albicans infections are more prevalent in obese individuals, which may result in inflammation of hair follicles, flexor surfaces and nail folds in the hands or feet.
“Our findings provide further evidence that obese patients are more susceptible to fungal-related skin diseases than normal individuals and that an elevation in BMI could lead to changes in fungal flora that adversely affect skin health.”
Impact on inflammation
In this study, the researchers observed that skin haemoglobin content increased significantly with a rise in BMI. Haemoglobin levels reflect vascular activity, and an increase in skin haemoglobin content often manifests as skin inflammation.
The inflammatory cytokines produced by adipose tissue and the activation of innate immune responses are considered key factors in obesity-induced inflammation.
“The abundances of differing bacterial genera, which would cause differences in metabolites and pro-inflammatory factors, may also have affected skin haemoglobin levels. These findings suggest that the epidermal barrier is fundamentally altered in the obese population, a phenomenon worth researching further.”
At the same time, obesity affects sebaceous and sweat gland secretion, and skin surface temperatures.
These impact the composition of skin lipids, which changes the environment in which microorganisms inhabit as well as the available nutrition, leading to alterations in microbial abundance and structure.
“We are inclined to conclude that when the skin microenvironment changes, which is reflected as variations in skin hydration, sebum and pH value, the abundances of bacteria alter accordingly. However, it is still unclear if these events are linked, and what the direction of causality is between them. This needs to be substantiated via additional studies.”
Source: Dove Medical Press
https://doi.org/10.2147/CCID.S447412
“Facial Physiological Characteristics and Skin Microbiomes Changes are Associated with Body Mass Index (BMI)”
Authors: Laiji Ma, et al
